1. Field of the Invention
The present invention relates to an optical disc onto which an information signal is recorded and to a reproduction apparatus for the disc. In more detail, the present invention relates to an optical disc used for recording multimedia data, such as digital video data, audio data, and graphics data, and to a reproduction apparatus for such optical disc.
2. Description of the Related Art
The achievement of large-capacity optical discs in recent years has led to a great deal of research into the development of multi-title optical discs. Here, the expression “multi-title” refers to the storage of a variety of video titles on a single disc to improve the cost-effectiveness of distribution and retailing of video titles, and, by doing so, increase the value-added of optical discs.
The expression “video titles” is used here to loosely refer to any video production which is represented by one or more sets of route information, which show the reproduction routes to be taken by an optical pickup when reading the optical disc, and sets of video information that are successively read by the optical pickup when tracing one of the reproduction routes. The video information referred to here is multiplexed data (usually referred to as an MPEG stream) which is made up of video data and audio data that have been subjected to compression at a high compression rate according to MPEG (Moving Pictures Experts Group) techniques.
FIG. 1 shows the structure of video titles which are recorded onto a multi-title optical disc. In this drawing, the expression “Single PGC” indicates titles which each only use one set of route information, while “Multi PGC” indicates titles which each include a plurality of sets of route information. The label “Loop present” indicates the presence of a loop attribute in the route information, with this attribute indicating the repetition of the retrieval of image information, while “No loop” indicates that no such loop attribute is present. Similarly, the label “Branch present” indicates the presence of conditional branch information in the route information, this conditional branch information indicating a branch to another set of route information which is performed interactively in response to a user operation.
In FIG. 1, the title for species (1) indicated by the labels “Single PGC”, “No branch”, and “No loop” is a single sequential title. A single sequential title refers to a title whose reproduction order is fixed according to one set of route information which has the title reproduced n order from the opening scene to the ending scene.
On the other hand, species (4), indicated by the labels “Multi PGC”, “No branch”, and “No loop”, is a multi-sequential title. Here, a multi-sequential title is a title which can be reproduced in a variety of reproduction orders according to a plurality of sets of route information, and so is not simply reproduced from start to end.
Species (2) and (3) indicated by the labels “Single PGC”, “No branch”, and “Loop present”, or “Multi PGC”, “No branch”, and “Loop present” are quiz-type titles. Quiz-type titles are video titles where the video information indicated by the route information is read many times in a random order. Examples of such quiz-type titles are aerobics titles and educational titles which use drills.
Species (5) and (6) indicated by the labels “Multi PGC”, “Branch present”, and “Automatic”, or by the labels “Multi PGC”, “Branch present” and “Interactive” correspond to titles which are known as “interactive titles”. Here, interactive titles are titles whose reproduction route dynamically changes in accordance with user operations made in response to menus that are displayed during the reproduction of the title.
The difference between interactive titles with the “Interactive” and “Automatic” labels is that “Automatic” interactive titles include a default reproduction route which is prepared beforehand for the case when no user selection operation of a branch destination is made.
The difference kinds of title in species (1) to (6) are classified depending on the number of reproduction routes, the existence of branch information, and the existence of loop attributes. Here, information for classifying the titles stored on an optical disc into these different types is generally referred to as the “formation” of a title.
The big disadvantage of storing different species (1) to (6) of video titles on a single optical disc is that a complex logical structure is required. Because of this complexity, it is difficult to achieve the reproduction features provided on conventional image reproduction apparatuses such as CD (Compact Disc), laser disc, or video CD players. Here, CD, laser disc, and video CD players are generally regarded as household AV (Audio-visual) appliances, with a search function and a feedback function being examples of the functions provided by such appliances which are problematic for multi-title discs.
The search function provided on a conventional AV appliance enables users to directly input a chapter number, song number, or expected reproduction time which may be written on the case of the disc, and by doing so instantly achieve reproduction of their desired data. The feedback function is a function which displays a chapter number, song number and/or present reproduction time to give the user real-time feedback showing what part of the data is presently being reproduced, with the reproduction time and chapter number being constantly updated as the reproduction of the disc progresses. These AV functions require the establishment of one-to-one correspondence between the disc storage address of a set of data and the chapter number, song number and/or present reproduction time of the set of data. For conventional CDs, video CDs, and laser discs, data is recorded sequentially on a spiral track, so that disc reproduction apparatuses have been able to know the present reproduction time and present chapter number by merely looking at the disc storage address of the data presently being reproduced. As a result, when a chapter number or reproduction time is directly inputted by the user, such reproduction devices have been able to directly jump to the data which corresponds to the user indication. In the following explanation, the case where a jump is performed to data indicated by the input of a reproduction time (so many minutes and seconds) by the user will be referred to as a “time search”, while the case when a jump is performed to data corresponding to an inputted chapter number will be referred to as a “chapter search”.
For a multi-title optical disc, there is no one-to-one correspondence between disc storage addresses of sets of data and chapter numbers/reproduction time. As a result, it is necessary for disc reproduction apparatuses of multi-title optical discs to perform emulated AV functions. Here, the expression “emulated AV functions” refers to the execution by multi-title disc reproduction apparatuses of functions whose results resemble those of the search function and feedback function of conventional disc players.
When a multi-title optical disc reproduction apparatus is instructed to reproduce a video title, the decision as to whether to perform emulated AV functions for the indicated video title is made based on the number of sets of route information, on the existence of branch information, on the existence of loop attributes, and on the relation between the memory size of the disc reproduction apparatus and the execution speed. Here, it is necessary for the disc reproduction apparatus to determine whether the title only includes one set of route information, whether loop information exists, whether automatic branches exist, and whether interactive branches exist. However, since loop information, automatic branch information, and interactive branch information are distributed across an optical disc, the determination of the presence of each of them takes a considerable amount of processing time.
The following is an explanation of an example operation when a user inserts a multi-title optical disc into the disc reproduction apparatus and indicates the reproduction of one of the titles on the disc. Here, in order to determine whether emulated AV functions can be performed for the selected title, the disc reproduction apparatus has to determine whether there is only one set of route information, whether loop information is present, whether any automatic branches are present, and whether any interactive branches are present. Here, the apparatus can only know whether loop attributes or branch information are included in the sets of route information by referring to all sets of route information used by the indicated title. Here, there is the possibility that even if a first set of route information does not include route information, a second or third set of route information may still include branch information, so that the reproduction apparatus must go to the trouble of referring to all of such sets of route information, thereby consuming a considerable amount of processing time.
The above example corresponds to a title classifying method (used by the present video CD standard) wherein branch information can be provided in sets of route information, although in interactive software developed in recent years, there is an increasing tendency for the provision of far more complex changes in image reproduction by providing route information which contains reproduction control information for performing branches and a variety of other forms of reproduction control.
Aside from the provision of reproduction control information in sets of route information, it is also possible to provide the same kind of reproduction control information in the management information interleaved into MPEG streams, or to distribute reproduction control information between MPEG management information and sets of route information, so that a great variety of story developments can be achieved. As a result, it becomes extremely difficult to detect reproduction control information which is distributed between so many locations to judge whether emulated AV functions are possible. Moreover, the reproduction of video data is performed for units which are several megabytes long, so that the investigation of reproduction control information is included in this kind of MPEG stream requires a memory capacity and disc seek speed which are well beyond the capability of economically-viable disc reproduction apparatuses.
In view of the difficulties when a plurality of titles are to be stored on a single optical disc, it has been suggested that AV functions should not be provided for any of the titles on a multi-title disc. However, in such a case, when viewing a same kind of title as was available for conventional video CD or laser disc, the user will not be able to make use of the AV functions to which he/she has become accustomed, thereby preventing jumps to a specified chapter number or reproduction time. This will not meet the user expectations for such reproduction and can potentially lead to user dissatisfaction with this kind of equipment.